Cystic fibrosis (CF) is a single gene defect which causes abnormal epithelial ion transport leading to airway obstruction and inflammation. Previous gene therapy methods have been transient and sometimes associated with inflammation. We have developed an alternative vector system, adeno-associated virus (AAV), which persists long-term without inflammation. In the current study, we hypothesize that an AAV-CFTR vector can be safely delivered to the nose and lung of adult CF patients and lead to gene transfer and correction of defective electrolyte transport. The study involves a single-dose,placebo-controlled, double-blinded, dose-escalation design. Three patients have been enrolled to date with no vector-related adverse effects.